There is an urgent demand for the development of innovative diagnostic and therapeutic products for widespread use in the bio-defense field, especially against Category A pathogens such as Bacillus anthracis. To this end it is desirable that the developed products show high specificity for their target and high stability to denaturation. Recent work identified a novel antibody isotype, called IgNAR (novel antigen receptor) in the serum of nurse sharks. This molecule is unusual as the variable (V) regions, responsible for binding antigen, did not form a dimer as in conventional antibodies but are able to bind antigen as individual soluble domains. Due to its high level of targeted somatic hypermutation IgNAR appears to be the molecule responsible for the true adaptive immune system in cartilaginous fish. The aim of this project is to isolate specific and highly stable single domain antibody fragments from nurse sharks immunized with the recombinant form of protective antigen (rPA) from B. anthracis. Due to the unique nature of these molecules, if this initial antigen proves successful, we envisage this technique will provide a platform technology which could easily be utilized to supply similar fragments for use as diagnostic or therapeutic tools for limitless other targets of interest for bio-defense. [unreadable] [unreadable] [unreadable] [unreadable]